In recent years, MEMS (Micro Electro Mechanical Systems) torsional hinged mirror structures have found significant application in telecommunication and free space optic systems such as optical switches and fiber optic replacement for broadband communications. Strides have also been made as replacements for spinning polygon mirrors used as the engine for high speed printers and some types of display systems. Such torsional hinged mirror structures have certain advantages over the systems they replace including high bandwidth, lower cost, and smaller volume. However, every new technology has its own set of problems and using torsional hinged mirrors in precision applications is no exception. One problem experienced by torsional hinged devices, such as mirrors, is excessive compressive loads or stresses on the torsional hinges due to the combination of temperature changes and significant differences in the TCE of the devices, and the TCE of the structure that supports the device. For example, the device is likely to be silicon, which has a very low TCE of approximately 3×10−6/° C. On the other hand, traditional substrate materials used for supporting devices, such as mirrors, have somewhat higher TCEs of approximately 6 to 20×10−6/° C. The silicon devices are typically assembled or bonded to the substrate with an adhesive, which is cured at approximately 125° C. However, when the silicon substrate assembly cools to the minimum specified temperature, the substrate shrinks substantially more than the silicon device, causing the device to be put in significant compressive loading. Sometimes, the low temperature exposure causes the hinges of the device to fail because of compressive buckling.
Previous efforts to solve these problems used ceramic substrates, which have a very low TCE somewhat comparable to the TCE of the silicon device itself. However, these ceramic substrates are expensive compared with other types of substrates and distract from the otherwise cost advantages of torsional hinged devices. Therefore, it will be appreciated that a method of controlling the TCE low temperature compressive loading and hinged device buckling while using inexpensive type substrates would be advantageous.